1. Field of the Invention
This invention relates to dental restoration structures and methods, and, more specifically, to dental matrix bands that may be bonded to resin-based filling materials and methods of using the same.
2. Description of the Related Art
Composite dental resins have many advantages over other restorative materials such as amalgam, a popular restorative material. When compared to amalgam, such resins are superior in color, smoothness and bondability. It is also noted that amalgams, unlike resins, contain mercury, a substance considered by many to be objectionable. Although composite resins are finding greater use, they are not without their problems. These problems include the following: (a) there are a high percentage of "open contacts" associated with interproximal composite restorations; (b) composite restorations are difficult to trim and finish; and (c) uncured composite resins stick to metal instruments.
With respect to problem (a) above, "open contacts" are usually the result of the space occupied by the matrix band during the process of restoration. More specifically, once an interproximal cavity has been prepared, a matrix band is placed around the tooth. After the band is placed, a wedge is pushed between the outer surface of the band and the adjacent tooth. The wedge serves a number of purposes. First, the wedge tightly compresses the band against the cervical margin of the cavity, i.e. the margin closest to the root. Secondly, the wedge forces the adjacent teeth apart. In an ideal interproximal restoration, the adjacent teeth will move back toward each other after the wedge and band are removed such that the adjacent tooth and the filling will passively abut. If the filling does not abut the adjacent tooth, there is a gap between the teeth known as an "open contact".
Those concerned with the development of dental equipment and methods have long recognized the need for restorative procedures and structures that reduce the number of "open contacts". For example, U.S. Pat. No. 2,035,347 is directed to a filling method that employs a strip of metal having a plurality of different sized spheroidal projections that may be used as contact points to close "open contacts". In the '347 patent, that portion of the metal strip having the appropriate sized contact point is placed in position against the filling immediately after the matrix band is removed. According to the '347 patent, "the free mercury in the filling will immediately amalgamate the metal in the surface of the fillet", i.e. the metal strip will bond to the filling with the contact point in place to close the "open contact".
Another solution to the "open-contact" problem is proposed in U.S. Pat. No. 4,778,385. In this patent, a collection of different sized composite matrix structures having convex and concave surfaces are preformed and supplied to the dentist. A matrix, sized to cover the proximal cavity and close the "open contact", is chosen from the supply and firmly placed against the proximal surface of the tooth using a wedge. The tooth is then filled with a composite restorative material that has the identical composition as the material from which the composite matrix is made. The composite material and a bonding agent, previously applied to the proximal surface of the tooth and the inner surface of the matrix, are now cured. The wedge is then removed and the process is finished. In some cases shrinkage of the matrix occurs resulting in exposed margins. In those cases, bonding agent is applied to the exposed margins and cured.
Although these devices have served the purpose, they are subject to some serious limitations. Both the '347 and '385 patents teach devices that are preformed, pre-shaped and not flexible. Hence, both patents teach structures that must be supplied to the dentist in multiple sizes and shapes in order to be useful thereby making the devices expensive to manufacture, and cumbersome to store and use. Furthermore, the '385 patent teaches a structure that must be made of the identical material as the filling material, another serious limitation on its use.
The use of a wedge in the '385 patent is still a further limitation. Its use, like most conventional wedges, can cause numerous problems, such as bleeding from the gums and matrix band deformation, which increase the difficulties in achieving a successful composite restoration. Also, there is no way to accurately measure the amount of separation, if any, produced by a wedge. Misjudgments in wedge placement can, therefore, result in a contact that is either too tight or open after the wedge is removed. Shrinkage of a preformed matrix after curing the agent and filling is still a further serious shortcoming in trying to avoid an "open contact" with prior art devices.
With respect to the trimming and finishing problem (problem (b) above), composite restorations are more difficult to trim and finish than amalgams. Amalgams are soft and plastic when trimming and finishing are performed. With composite resins, there is no intermediary plastic state prior to hardening that allows easy trimming and finishing. As such, with resin-based restorations, the trimming and finishing process is tedious, delicate and time consuming. Therefore, those skilled in these arts have long sought devices and methods for use in resin-based restorations that reduce the amount of trimming and finishing necessary to complete a restoration.
Because of the sticking problem (problem (c) above), i.e. uncured composite resins stick to metal instruments, dentists are often required to have a second set of instruments for working with composite resins in addition to the standard metal instruments. For example, when performing the process disclosed in the '385 patent, the dentist should have a special instrument with a non-metal surface (e.g. teflon coated) for use in filling the void, i.e. during condensing of the composite restoration material in order to avoid sticking problems. Besides being expensive, the need for additional instruments makes the process more complicated to perform.
As such, present devices and methods for performing restorations with composite resins have problems that result in a number of serious limitations. The present invention mitigates these problems.